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Simple Summary: With the increasing threat that mosquito borne diseases pose to public health, the demand for environmentally sustainable pesticides has been increasing in recent years. Pesticides that target the larval stage (i.e., larvicides) are particularly useful for controlling mosquito populations as they strike at the source. Currently, Bacillus thuringiensis subspecies israelensis (BTI) is a commonly used mosquito larvicide but some studies show signs of resistance development. DL-methionine is an essential amino acid that has mosquito larvicidal capabilities, while also having minimal negative effects on non-target organisms in laboratory experiments. In this study, our objective was to evaluate the effect of these two larvicides individually and together at reducing mosquito survival. We found that while DL-methionine was more toxic to Anopheles quadrimaculatus than Aedes aegypti, the opposite was true for BTI. Additionally, when the combination was tested against An. quadrimaculatus larvae at higher concentrations the active ingredients were complementary and the effect was equal to both ingredients alone. However, the active ingredients were antagonistic when tested against Ae. aegypti larvae. These findings are important as they show the potential for DL-methionine and the combination of DL-methionine with BTI to be used as a larvicide against Anopheles mosquitoes, which are responsible for transmitting malaria. Mosquito larvicides can reduce mosquito populations at the source, potentially decreasing biting rates and pathogen transmission. However, there is a growing need for mosquito larvicides that are environmentally sustainable. Bacillus thuringiensis subspecies israelensis (BTI) is a naturally occurring bacterium commonly used as a larvicide to manage mosquito populations. Methionine is an essential amino acid that has demonstrated toxic properties against larval mosquitoes in laboratory experiments, while having minimal effects on non-target organisms. The goal of this study was to evaluate the potential for a novel combination larvicide by testing for compatibility between these two active ingredients. We began by determining the lethal concentration values (LCs) of BTI and DL-methionine against Anopheles quadrimaculatus Say and Aedes aegypti Linnaeus (Diptera: Culicidae) larvae. These bioassays were conducted in glass jars and mortality was observed 48 h post-treatment. We found that while DL-methionine was more toxic to An. quadrimaculatus than Ae. aegypti, the opposite was true for BTI. Then, we used these LCs to conduct bioassays with a combination of BTI and DL-methionine to determine the relationship between the two active ingredients when used against An. quadrimaculatus and Ae. aegypti larvae. The findings of this study demonstrate that BTI and DL-methionine have the potential to be complementary due to their additive properties at higher concentrations and effect levels when tested against An. quadrimaculatus. However, an antagonistic relationship was detected at the concentrations tested with Ae. aegypti. These results are encouraging and imply that a DL-methionine or BTI/DL-methionine combination larvicide could be used in management of Anopheles species. [ABSTRACT FROM AUTHOR]

Methionine is a naturally occurring amino acid that has demonstrated toxic properties for control of larval mosquitoes in laboratory experiments. Methionine offers many desirable qualities for an effective, biorational pesticide, including its minimal effects on non-target species. Because previous studies regarding this amino acid's toxicity were laboratory based, the next step is to establish if methionine is likely to have similar effects in natural water bodies before attempting costly field trials. Therefore, the goal of this study was to test the effectiveness of DL-methionine applied to various water sources. Concentration response experiments conducted in glass jars used larval Aedes aegypti (L.) (Diptera: Culicidae) as a model organism. Well, deionized, and pond water were evaluated in the study. In general, increased mortality of Ae. aegypti larvae occurred with increasing concentrations of DL-methionine at 48 h. However, larval DL-methionine LC50 values were not different between water sources. This study has shown that DL-methionine can be added to various water sources as a possible biorational larvicide when applied to natural water sources such as ponds or water-holding containers that often are preferred larval developmental sites for a variety of mosquito disease vectors. [ABSTRACT FROM AUTHOR]